Microfluidic systems are highly useful in medical diagnostics, environmental monitorings, biological food testing, chemical sensing and analysis. Current efforts on the fabrication of microfluidic systems and fluidic technologies have been mainly focused on individual component development. Individual components such as pumps [See M. Esashi et al. "Normally Close Microvalve and Micropump Fabricated on a Silicon Wafer," in International Workshop on Micro Electromechanical Systems (MEMS 89), pp. 29-34 (1989); R. Zengerie et al., "A Micro Membrane Pump with Electrostatic Actuation," in International Workshop on Micro Electromechanical Systems (MEMS 92), pp. 19-24 (1992); W. Zang and C. H. Ahn, "A Bi-directional Magnetic Micropump on a Silicon Wafer," in International Workshop on Solid-State Sensors and Actuators (Hilton Head '96), pp. 94-97 (1996)], valves [See T. Ohnstein et al., "Michromachined Silicon Valve," in International Workshop on Solid-State Sensors and Actuators (Hilton Head '90), pp. 95-97 (1990); J. G. Smith, "Piezoelectric Micropump with Three Valves Working Peristaltically, "Sensors and Actuators, Vol. A21-23, pp. 203-206 (1990); Y. -C Lin et al., "Characteristics of a Polyamide Microvalve," in International Workshop on Solid-State Sensors and Actuators (Hilton Head '96), pp. 113-116 (1996)], fluidic channels [J. Pfahler et al., "Liquid Transport in Micron and Submicron Channels," Sensors and Actuators, Vol. A21-23, pp. 431-434 (1990)], reaction chambers [S. Nakagawa et al., "A Micro Chemical Analyzing System Integrated on a Silicon Wafer," in International Workshop on Solid-State Sensors and Actuators (Hilton Head '90), pp. 89-94 (1990)], separation stages [D. J. Harrison et al., "Chemical Analysis and Electrophoresis Systems Integrated on Glass and Silicon Chips," in International Workshop on Solid-State Sensors and Actuators (Hilton Head '92), pp. 110-113 (1992); A. Manz et al.," Integrated Electroosmotic Pumps and Flow Manifolds for Total Chemical Analysis Systems," in Transducers '91, pp. 939-941 (1991); A. Manz et al., "Planar Chips Technology for Miniaturization and Integration of Separation Techniques into Monitoring Systems: Capillary Electrophoresis on a Chip," J. Chromatography, Vol. 593, pp. 253-258 (1992)] and detection techniques [R. C. Anderson, G. J. Bodgdan and R. J. Lipshutz, "Miniaturized Genetic Analysis System," in International Workshop on Solid-State Sensors and Actuators (Hilton Head '96), pp. 258-261 (1996)], have been fabricated using a sundry of technologies. Numerous fluidic propulsional methods have also been developed based on mechanical pumping, pneumatic forces, electrosmosis [D. J. Harrison et al., "Miniaturized Chemical Analysis Systems Based on Electrophoretic Separations and Electrosmotic Pumping," in Transducers '93, pp. 403-406 (1993)], dielectrophoresis [H. A. Pohl, Dielectrophoresis, Cambridge: Cambridge University Press (1978)], surface tension gradients [M. A. Burns et al., "Microfabricated Structures for Integrated DNA Analysis," Proc. Natl. Acad. Sci. USA, 93:5556-5561 (1996); H. Matsumoto and J. E. Colgate, "Preliminary Investigation of Micropumping Based on Electrical Control of Interfacial Tension," in International Workshop on Solid-State Sensors and Actuators (Hilton Head '90), pp. 105-110 (1990); G. Beni and M. A. Tenan, "Dynamics of Electrowetting Displays," J. Appl. Phys., Vol. 52, pp. 6011-6015 (1981), bubble generation [L. Lin et al., "Microbubble Powered Actuator," in Transducers '91, pp. 1041-1044 (1991)], and evaporation-condensation [T. K. Jun and C. J. Kim, "Miscroscale Pumping with Traversing Bubbles in Microchannels," in International Workshop on Solid-State Sensors and Actuators (Hilton Head '96), pp. 144-147 (1996)].
However, efforts on system integration of components to date have been limited [S. C. Terry et al., "A Gas Chromatographic Air Analyzer Fabricated on a Silicon Wafer," IEEE Trans. on Electron Devices, Vol. ED-26, pp. 1880-1886 (1979); A. van der Berg and P. Bergveld, Micro Total Analysis Systems, New York: Kluwer (1994)], which mainly include the use of bulk micromachining and surface micromachining technology. Both of them lack simple construction of components and the capability to integrate all of components with electronic circuitry.
Bulk micromachining technology, which includes the use of glass wafer processing, silicon-to-glass wafer bonding, has been commonly used to fabricate individual microfluidic components. In Europe, this glass-bonding technology has also been used to fabricate microfluidic systems. In these systems, the control electronics are implemented on a hybrid manner external to the system. This system integration method has several problems. Because these systems rely on bonding of substrates, it is essential that the bonding surfaces create an hermetic seal to prevent the leakage of chemicals and reagents. This poses a great difficulty when interconnection leads are present on the bonding surfaces which prevent the surfaces from being flat. It is well known that it is exceedingly difficult to attain good bonds even using well-characterized techniques such as anodic bonding when steps on the bonding surfaces exceed 0.2 .mu.m. Because of this planarity requirement, these devices require either complex planarization schemes, or the use of diffused leads. Because of these difficulties, only relatively simple fluidic systems can be constructed using this scheme.
Unlike bulk micromachining, surface micromachining technology can be used to fabricate individual fluidic components as well as microfluidic systems with on-chip electronics. In addition, unlike bonded-type devices, hermetic channels can be built in a relatively simple manner using channel walls made of polysilicon [J. R. Webster et al., "Monolithic Capillary Gel Electrophoresis Stage with On-Chip Detector," in International Conference on Micro Electromechanical Systems (MEMS 96), pp. 491-496 (1996)], silicon nitride [C. H. Mastrangelo and R. S. Mullet, "Vacuum-Sealed Silicon Micromachined Incandescent Light Source," in Inl. Electron Devices Meeting (IDEM 89), pp. 503-506 (1989)] and silicon dioxide. Surface micromachined channels that are constructed with these thin films have two basic problems. Because the thickness of the films is limited to a few microns, the height of cavities and channels is very small (&lt;5 .mu.m) resulting in sub-pL sample volumes. These exceedingly small sample volumes both strain the requirements for the sensitivity limits of detection schemes and also aggravate the surface adsorption of samples and reagents on the wall which further diminishes the sample concentration. On the fabrication side, due to the strong nature of the silicon based building materials, the formation of long capillaries is difficult to accomplish. This is because the etchants used for the sacrificial etch are relatively slow and in may cases extremely reactive (such as hydrofluoric acid HF). In these structures, it is customary to leave devices in the sacrificial etch solution for many hours. Special passivation layers (primarily silicon nitride SiN) are used to passivate any active electronic devices that must survive the sacrificial etch.
What is needed is micromachining technology that allows for fabrication of channels with a flexibility in cross section and channel length at virtually no loss in system performance. In addition, the polymer technology should be low cost and should not require specialized equipment.